Self-assembled nanoparticle arrays as nanomasks for pattern transfer

Abstract

Argon ion milling was used to transfer the pattern of sparse 12 nm iron oxide nanoparticles into underlying thin films of Pt and magnetic tunnel junction stacks and quantify their etching rates and morphological evolution. Under typical milling conditions, Pt milled at 10 nm min−1, while the isolated particles of iron oxide used for the mask milled at 5 nm min−1. Dilute dispersions of nanoparticles were used to produce the sparse nanomasks, and high resolution scanning electron microscopy (SEM) and atomic force microscopy were used to monitor the evolution of etched structures as a function of milling time. SEM measurements indicate an apparent 20% increase in feature diameter before the features began to diminish under additional milling, suggesting redeposition as a limiting feature in the milling of dense arrays. Simulations of the milling process in nanoparticle arrays that include redeposition are consistent with this observation. These simulations predict that an edge-to-edge spacing of 3 nm in a dense array is feasible, but that redeposition reduces the final structure aspect ratio from that of the masking array by as much as a factor of two.

Ultra-Large-Area Self-Assembled Monolayers of Nanoparticles

“…Advances in nanoparticle (NP) synthesis using high boiling point organic solvent have vastly improved the control of size and shape uniformity. − The surfactant coating of these particles forms a steric barrier that prevents irreversible agglomeration of the inorganic cores. This provides the particles with the mobility needed to adjust their relative positions until they form a low-energy, self-organized pattern, such as 2D monolayers − or 3D crystals. − Among those nanopatterns, monolayers of NP assemblies are of significant technical importance in fields such as catalysis, sensors, nanoelectronics, − and bit-patterned magnetic media, − as well as in fundamental research . However, it is a significant challenge to obtain large-area (∼centimeter scale) monolayers without discontinuities .…”

Spin transfer torque switching of magnetic tunnel junctions using a conductive atomic force microscope

“…2 The devices in this previous work have used fixed leads for characterization, but fixed leads will present serious challenges if MTJs are to be used for data storage with several terabit per square inch data density. 3,4 Other groups have previously investigated the use of scanning probes for information storage. The IBM Millipede project 5 with dense arrays of scanning probes used a thermomechanical approach to read and write bits with a special resistive heater probe to controllably deform a thin polymer film.…”

Pattern transfer with stabilized nanoparticle etch masks

“…Three techniques have been used to remove surfactant coatings from nanoparticles. The first is heating in a partial vacuum to remove gas phase byproducts [16]. Weakly bound oleic acid starts to desorb at 200 • C and dehydrogenation begins above 400 • C [17].…”